let's say is "x", so, then "x" is the 100%, and we know that the 60% is 120, what the dickens is "x" anyway?
[tex]\bf \begin{array}{ccll}
marks&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
x&100\\
120&60
\end{array}\implies \cfrac{x}{120}=\cfrac{100}{60}\implies x=\cfrac{120\cdot 100}{60}[/tex]
